1. Field of the Invention
The present invention relates to the field of heat sinks for semiconductor devices and integrated circuits.
2. Prior Art
Various configurations of heat sinks for semiconductor devices and integrated circuits are well known in the prior art. One common type of heat sink for mounting on the integrated circuit or other semiconductor device comprises a heat sink having projecting fins or legs to increase the surface area of the heat sink for heat dissipation to the surrounding area, either through free convection or forced convection (fan driven) cooling.
In some cases, heat sinks have been configured to somehow snap onto the integrated circuit or other semiconductor device. In such circumstances, the thermal contact between the integrated circuit and the heat sink can be substantially limited, as the actual area of contact between the integrated circuit and the heat sink can be only a small fraction of a potential area for such contact. In such cases, the heat transfer from the integrated circuit to the heat sink may be increased through the use of a thermally conductive grease spanning the air spaces between the heat sink and the packaged integrated circuit. In other cases, the heat sinks have been cemented to the packaged integrated circuits, providing both the mounting and the substantial absence of air spaces between the packaged integrated circuits and the heat sinks.
In the foregoing type of heat sinks, even with very good thermal coupling between the integrated circuit and the heat sink, there frequently is a substantial differential temperature between the integrated circuit and the cooling fins or protrusions on the heat sink, particularly in the larger integrated circuits having a high power dissipation per unit area. Further, integrated circuits having a high power dissipation per unit area tend to run hotter in the center of the integrated circuit than at the edges of the integrated circuit because of the lateral flow of heat away from the edges of the silicon chip. This temperature difference across the chip is undesirable, as even identical transistors operating at different temperatures have different characteristics. The temperature differentials across the chip also mechanically stress the chip, and also allow part of the chip to run hotter than it otherwise would if the temperature was more evenly distributed.
Heat pipes are also well known devices for transferring heat from a warmer location to a cooler location. A typical heat pipe is comprised of an appropriately shaped heat conductive enclosure which has been partially filled with an appropriate liquid. In operation, the liquid in the portion of the heat pipe adjacent the hotter area of the heat pipe absorbs heat and turns to gas, with the gas adjacent the cooler area of the heat pipe condensing back to liquid form to flow back to the hotter area of the heat pipe. Thus, a flow of gas is established from the hotter portion of the heat pipe to the cooler portion of the heat pipe, and a corresponding flow of liquid is established back from the cooler portion of the heat pipe to the hotter portion of the heat pipe. Thus, the heat transfer achieved through the use of the heat pipe is primarily a result of the mass transfer occurring within the heat pipe automatically as a result of the differential temperature between the ends of the heat pipe.
Modular heat sinks utilizing heat pipes to provide a more uniform temperature distribution over a packaged integrated circuit and efficient heat sinking in either free or forced convection environments. The heat sinks utilize both horizontal and vertical heat pipes to transfer heat both horizontally and vertically in the heat sinks. Selection of the number of heat pipes used allows tailoring of the heat sink capabilities for different applications using the same fundamental assemblage of parts.
One of the important enhancements of this invention is the ability to provide uniform and even heat flux (power density) distribution. This particular functionality reduces high junction temperature in a semiconductor (or any power) device (ASICs, microprocessors, power and laser devices, etc.). This functionality will also enhance and reduce the cooling requirements for these devices because of the heat flux per unit area (i.e., power density) reduction.
The volumetric and surface area heat flux distribution is determined by the number and spacing of these heat pipes in both lateral and axial directions, and the available cooling medium. In most cases, for low power devices, the application of this invention will be sufficient to cool devices by natural convection.
Various embodiments and fabrication techniques are disclosed, including both heat sinks having directional and non directional convection current dependency.